Various arrangements for memory chips in a memory system have been proposed. For example, in a typical synchronous dynamic random access memory (SDRAM) system, memory chips communicate data through bidirectional data buses and receive commands and addresses through command and addresses buses. The memory chips have stubs that connect to the buses in a multi-drop configuration (coupling three or more points). Other designs include point-to-point signaling (coupling two points). The point-to-point signaling may be unidirectional or bidirectional. The signaling may be single ended or differential. In some systems, address, command, and write data may be on the same conductors.
Many computer systems include a motherboard to which various chips and connectors are attached. Motherboards are typically printed circuit boards (PCBs). Conductors between chips and connectors on the motherboard are either on the surface of the motherboard or in between layers of the motherboard. The conductors may be formed of a different materials including, for example, vias between layers.
The connectors on the motherboards receive cards which are typically PCBs. Examples of the cards are memory modules and continuity modules. Memory modules include a substrate supporting memory chips on one or both sides of the substrate. A dual-in line memory module (DIMM) is an example of a memory module. When a memory module is not used, a continuity module is sometimes inserted in a connector to terminate signals or to connect conductors to other conductors. Memory modules may also include termination circuits to terminate signals received by the memory modules. The connectors typically include pads or other conductive surfaces to receive fingers or other conductive surfaces of the memory or continuity modules. For various reasons (such as cost, technological, or standard reasons), there can be limits on the number of fingers or conductive surfaces on the connector and modules.
Some computer systems having included some memory chips on a motherboard and other memory chips on a memory module or other card in a connector on the motherboard.
A channel includes a group of conductors between the memory controller and memory chips. There may be a series of memory chips on a channel. Some memory systems have one channel and some more than one channel with modules in parallel. Modules may be in series.
Ranks refer to memory chips that are accessed together. More than one rank can be put on a memory module, but additional ranks per module can be expensive.
In some memory systems, the memory chips receive signals and repeat them to other memory chips as well as provide requested data signals to next memory chips. The data signals can be provided to the memory controller through point-to-point unidirectional return links that are repeated back or return in a looped fashion from a last memory chip.
Memory controllers have been used in chipset hubs and in a chip that includes a processor core. Some computer systems include wireless transmitter and receiver circuits.